The research program is intended to provide information on the mechanism of action of the visual receptor complex in the initiation, adaptation, and maintenance of vision. An understanding of how light is translated to an electrical signal in vision may also be relevant to an understanding of the mechanism of operation of other sensory or receptor processes, such as taste, hearing, pain, etc., and hormone events. In order to obtain the required information, a variety of techniques have been used. Information has been obtained on the ionization changes of the visual pigment rhodopsin, on the sulfhydryl groups of rhodopsin, and on the sequences of thermal intermediates in solution and intact retina. Studies on visually deficient Drosophila mutants have revealed differences in visual pigment and other proteins. Direct studies intended to correlate visual pigment changes and electrical changes in the eye have also been performed. Simultaneous measurements of spectral and electrical changes indicated a correspondence between the metarhodopsin I478 to II380 reaction and the early receptor potential. As revealed by artificial membrane, pH, and buffer studies, the ionization changes of the reaction or accompanying pH changes, affect the permeability of the vertebrate photoreceptor, and may be a part of the phototransduction process.